Motor vehicle drive trains generally include a substantially tubular drive shaft and one or more axles driven through a differential mechanism. Collectively, this drive train is driven by a prime mover, such as an engine, through a transmission. Drive shafts, sometimes referred to as propeller shafts, are remarkably simple mechanically but are a vital element of the drive train. It has long been recognized that balancing of the drive shaft is a key element in improving the overall performance of the drive train. A well-balanced drive shaft results in a motor vehicle which is smoother and quieter. In addition, reducing or removing excessive vibration in the drive shaft contributes to increased component life of the remaining components in both the drive shaft and motor vehicle.
A wide variety of methodologies have been developed for the automated testing and balancing of tubular drive shaft elements. Modern computers, by virtue of their low cost and versatility, have become commonplace components in the process of drive shaft balancing. Utilizing testing equipment which is capable of determining the precise angular position of a drive shaft in relation to a test fixture, it is possible to analyze the vibrational signature of a drive shaft with exquisite precision. The information generated by such computers can then be fed back to an operator or automated machine to assist in the precise location of counterweights in relation to the drive shaft, thereby minimizing its tendency to vibrate over a wide range of speeds and operating conditions.
The existing methodologies all generally involve placement of a drive shaft or similar rotating element in a fixture similar to an ordinary lathe. The drive shaft is suspended from spindles on opposing ends of the machine, and rotated rapidly on the spindles utilizing well-known power means. Sensors associated with the spindles determine an out-of-balance condition and provide a computer display or printout of the angular position on the shaft corresponding to an imbalance. Modern computers in this application are also programmed to identify the amount of the counterweight required in order to bring the shaft into balance. In other words, both the position of the imbalance and the mass and location of the necessary counterweight are provided by the associated computer.
In the current state of the art, individual weights of varying sizes and masses are attached to the shaft by projection welding. Such weights have small “feet” or projections which facilitate the attachment of the weight to the outer surface of the shaft. The weights themselves are generally small rectangular elements having a curvature which matches or approximates the curvature of the outer circumference of the shaft. In the current state of the art an operator either manually positions, or instructs a robotic element to position the necessary weight on the propeller or drive shaft in an appropriate position in relation to the out-of-balance position. The required weights are then secured to the propeller shaft by an automated welding device. This process may require the positioning of one or more weights of varying sizes in different angular positions on the circumference of the shaft. Once the welding operations are completed, the shaft may again be tested to verify that the weight positioning is correct.
In the current state of the art, the task is work-intensive, requiring the operator to frequently stop and start the balancer, determine the proper location for the weights, locate suitable size and mass of weights, manually position the weights on the shaft, operate the welding apparatus for securing the weights to the shaft and then verify the positioning. Numerous efforts have been made over the years to automate this process. Recently, one of the inventors of the present invention has filed a patent application for an improved apparatus for shaft-balancing using an automated process and a collection of standardized weights as described in the co-pending application Ser. No. 10/739,365.
Additional improvements to the machines for performing the balancing and welding tasks have been developed recently, including machines which will automatically feed and place custom-formed weights and weld them to the shaft being balanced. Problems exist, however, in that the welding heads associated with this type of equipment are fixed in relation to the position of the drive shaft, limiting the longitudinal position of the shaft on which the weight can be placed, and further limiting the relationship of the position of weights which can be disposed about the circumference of and along the longitudinal axis of the shaft to be balanced. Further, existing welding equipment is bulky and surrounds the shaft to position positive and negative electrodes on opposite sides of the shaft. This restricts the ability to position the welding head along the length of the shaft.
It has been learned that substantially improved drive shaft balancing can be achieved by the utilization of side-by-side welding electrodes which can be selectively positioned in relation to the longitudinal axis of the drive shaft, as the welding device is positioned under computer control.
What is needed then, is a welding apparatus wherein the stations for forming and welding the weights can be easily and continuously positioned along the same longitudinal axis utilized by the balancing machine for the drive shafts being balanced.